Since the discovery of serotonin (5-hydroxytryptamine, 5-HT) over four decades ago, the cumulative results of many diverse studies have indicated that serotonin plays a significant role in the functioning of the mammalian body, both in the central nervous system and in peripheral systems as well. Morphological studies of the central nervous system have shown that serotonergic neurons, which originate in the brain stem, form a very diffuse system that projects to most areas of the brain and spinal cord. R. A. O'Brien, Serotonin in Mental Abnormalities, 1:41 (1978); H. W. M. Steinbusch, HANDBOOK OF CHEMICAL NEUROANATOMY, Volume 3, Part II, 68 (1984); N. E. Anden, et al., Acta Physiologica Scandinavia, 67:313 (1966). These studies have been complemented by biochemical evidence that indicates large concentrations of 5-HT exist in the brain and spinal cord. H. W. M. Steinbusch, supra.
With such a diffuse system, it is not surprising that 5-HT has been implicated as being involved in the expression of a number of behaviors, physiological responses, and diseases which originate in the central nervous system. These include such diverse areas as sleeping, eating, perceiving pain, controlling body temperature, controlling blood pressure, depression, schizophrenia, and other bodily states. R. W. Fuller, BIOLOGY OF SEROTONERGIC TRANSMISSION, 221 (1982); D. J. Boullin, SEROTONIN IN MENTAL ABNORMALITIES 1:316 (1978); J. Barchas, et al., Serotonin and Behavior, (1973).
Serotonin plays an important role in peripheral systems as well. For example, approximately 90% of the body's serotonin is synthesized in the gastrointestinal system, and serotonin has been found to mediate a variety of contractile, secretory, and electrophysiologic effects in this system. Serotonin may be taken up by the platelets and, upon platelet aggregation, be released such that the cardiovascular system provides another example of a peripheral network that is very sensitive to serotonin. Given the broad distribution of serotonin within the body, it is understandable that tremendous interest in drugs that affect serotonergic systems exists. In particular, receptor-specific agonists and antagonists are of interest for the treatment of a wide range of disorders, including anxiety, depression, hypertension, migraine, compulsive disorders, schizophrenia, autism, neurodegenerative disorders, such as Alzheimer's disease, Parkinsonism, and Huntington's chorea, and cancer chemotherapy-induced vomiting. M. D. Gershon, et al., THE PERIPHERAL ACTIONS OF 5-HYDROXYTRYPTAMINE, 246 (1989); P. R. Saxena, et al., Journal of Cardiovascular Pharmacology, 15:Supplement 7 (1990).
Serotonin produces its effects on cellular physiology by binding to specialized receptors on the cell surface. It is now recognized that multiple types of receptors exist for many neurotransmitters and hormones, including serotonin. The existence of multiple, structurally distinct serotonin receptors has provided the possibility that subtype-selective pharmacological agents can be produced. The development of such compounds could result in new and increasingly selective therapeutic agents with fewer side effects, since activation of individual receptor subtypes may function to affect specific actions of the different parts of the central and/or peripheral serotonergic systems.
An example of such specificity can be demonstrated by using the vascular system as an example. In certain blood vessels, stimulation of 5-HT.sub.1 -like receptors on the endothelial cells produces vasodilation while stimulation of 5-HT.sub.2 receptors on the smooth muscle cells produces vasoconstriction.
Currently, the major classes of serotonin receptors (5-HT.sub.1, 5-HT.sub.2, 5-HT.sub.3, 5-HT.sub.4, 5-HT.sub.5, 5-HT.sub.6, and 5-HT.sub.7) contain some fourteen to eighteen separate receptors that have been formally classified based on their pharmacological or structural differences. For an excellent review of the pharmacological effects and clinical implications of the various 5-HT receptor types, see Glennon, et al., Neuroscience and Behavioral Reviews, 14:35 (1990).!
Tachykinins are a family of peptides which share a common amidated carboxy terminal sequence. Substance P was the first peptide of this family to be isolated, although its purification and the determination of its primary sequence did not occur until the early 1970's.
Between 1983 and 1984 several groups reported the isolation of two novel mammalian tachykinins, now termed neurokinin A (also known as substance K, neuromedin L, and neurokinin .alpha.), and neurokinin B (also known as neuromedin K and neurokinin .beta.). See, J. E. Maggio, Peptides, 6 (Supplement 3):237-243 (1985) for a review of these discoveries.
Tachykinins are widely distributed in both the central and peripheral nervous systems, are released from nerves, and exert a variety of biological actions, which, in most cases, depend upon activation of specific receptors expressed on the membrane of target cells. Tachykinins are also produced by a number of non-neural tissues.
The mammalian tachykinins substance P, neurokinin A, and neurokinin B act through three major receptor subtypes, denoted as NK-1, NK-2, and NK-3, respectively. These receptors are present in a variety of organs.
Substance P is believed inter alia to be involved in the neurotransmission of pain sensations, including the pain associated with migraine headaches and with arthritis. These peptides have also been implicated in gastrointestinal disorders and diseases of the gastrointestinal tract such as inflammatory bowel disease. Tachykinins have also been implicated as playing a role in numerous other maladies, as discussed infra.
Tachykinins play a major role in mediating the sensation and transmission of pain or nociception, especially migraine headaches, see, e.g., S. L. Shepheard, et al., British Journal of Pharmacology, 108:11-20 (1993); S. M. Moussaoui, et al., European Journal of Pharmacology, 238:421-424 (1993); and W. S. Lee, et al., British Journal of Pharmacology, 112:920-924 (1994).
In view of the wide number of clinical maladies associated with an excess of tachykinins, the development of tachykinin receptor antagonists will serve to control these clinical conditions. The earliest tachykinin receptor antagonists were peptide derivatives. These antagonists proved to be of limited pharmaceutical utility because of their metabolic instability.
Recent publications have described novel classes of non-peptidyl tachykinin receptor antagonists which generally have greater oral bioavailability and metabolic stability than the earlier classes of tachykinin receptor antagonists. Examples of such newer non-peptidyl tachykinin receptor antagonists are found in U.S. Pat. No. 5,491,140, issued Feb. 13, 1996; U.S. Pat. No. 5,328,927, issued Jul. 12, 1994; U.S. Pat. No. 5,360,820, issued Nov. 1, 1994; U.S. Pat. No. 5,344,830, issued Sep. 6, 1994; U.S. Pat. No. 5,331,089, issued Jul. 19, 1994; European Patent Publication 591,040 A1, published Apr. 6, 1994; Patent Cooperation Treaty publication WO 94/01402, published Jan. 20, 1994; Patent Cooperation Treaty publication WO 94/04494, published Mar. 3, 1994; Patent Cooperation Treaty publication WO 93/011609, published Jan. 21, 1993; Canadian Patent Application 2154116, published Jan. 23, 1996; European Patent Publication 693,489, published Jan. 24, 1996; and Canadian Patent Application 2151116, published Dec. 11, 1995.
Patent Cooperation Treaty Patent Publication WO 96/11000, published Apr. 18, 1996 and European Patent Publication EP 705,600, published Apr. 10, 1996, describe a synergistic effect on the combination of a serotonin agonist and a tachykinin receptor antagonist in treating migraine. U.S. patent application Ser. No. 08/387,056, filed Feb. 10, 1995, now abandoned, describes a synergistic effect on the combination of a serotonin agonist and a tachykinin receptor antagonist in treating a variety of psychiatric disorders. U.S. patent application Ser. No. 08/408,238, filed Mar. 22, 1995, now abandoned, describes a synergistic effect on the combination of a serotonin agonist and a tachykinin receptor antagonist in treating a variety of types of pain and nociception. U.S. patent application Ser. No. 60/000074, filed Jun. 8, 1995, describes a synergistic effect on the combination of a serotonin agonist and a tachykinin receptor antagonist in treating the common cold or allergic rhinitis.
European Patent Application 0 577 394, published Jan. 5, 1994, teaches a series of morpholinyl and thiomorpholinyl tachykinin receptor antagonists. Patent Cooperation Treaty Patent Application WO 95/18124, published Jul. 6, 1995, teaches another series of substituted morpholines for use as tachykinin receptor antagonists. None of these references, nor any combination of them, teach the tachykinin receptor antagonists of the present invention.
In essence, this invention provides a class of potent non-peptidyl tachykinin receptor antagonists. By virtue of their non-peptide nature, the compounds of the present invention do not suffer from the shortcomings, in terms of metabolic instability, of known peptide-based tachykinin receptor antagonists.